Growth of Ge quantum dot at the mix-crystal interface self-induced on the ion beam sputtering deposition

The dense domes of Ge quantum dots on Si (001) substrate with a monomodal morphology distribution are deposited at different temperatures by ion beam sputtering (IBS). The areal density of the Ge quantum dots is observed to increase with elevating temperature, but the dots size to decrease. As the deposition temperature increases to 750 ℃, the smaller Ge quantum dots each with a height of 14.5 nm and base width of 52.7 nm are obtained by sputtering 15 monolayer Ge coverage, and the dots areal density is up to 1.681010 cm-2 at the same time. Thus the evolution of Ge quantum dot prepared by IBS is very different from that by vapor deposition at thermal equilibrium condition. The stable shape and the size distribution are demonstrated to result from the kinetic behavior of the surface atoms which is restricted by the thermodynamic limitations. A mix-crystal interface including amorphous and crystal components is revealed by Raman spectrum, and this special interface is demonstrated to contribute to the high density of Ge quantum dots, since the boundaries between the two different components can provide more preferential centers for the nucleation. As the density increases at high deposition temperature, the elastic repulsion between islands is enhanced, resulting in the surface atoms growing along the orientation of high index during the IBS deposition, and inducing the increase in aspect ratio and the reduction in island size.